As tensions mount between America and China over the South China Sea, the US Navy has sent an aircraft carrier into the disputed waterway.

The Navy announced the deployment of the USS Carl Vinson and guided-missile destroyer USS Wayne E. Meyer to the South China Sea on what it called “routine operations” in a statement released Saturday, despite warnings from Chinese officials not to challenge their sovereignty.

“China respects and upholds the freedom of navigation and overflight in the South China Sea, which countries enjoy under international law, but firmly opposes any country’s attempt to undermine China’s sovereignty and security in the name of the freedom of navigation and overflight,” said China’s Foreign Ministry spokesman Geng Shuang.

Beijing claims most of the South China Sea, where it has built artificial islands equipped with military weapons.

An international court in the Hague condemned those claims in July, but China does not recognize the ruling.

Earlier this month, US Defense Secretary James Mattis criticized China’s military buildup in the region and reaffirmed the US’s commitment to protect its ally Japan.

“I made clear that our longstanding policy on the [Japanese-controlled] Senkaku Islands stands — the US will continue to recognize Japanese administration of the islands and as such Article 5 of the US-Japan Security Treaty applies,” Mattis said during an appearance in Tokyo with Japanese Defense Minister Tomomi Inada.

Mattis also urged a more diplomatic approach.

“What we have to do is exhaust all efforts, diplomatic efforts, to try to resolve this properly, maintaining open lines of communication,” he said. “At this time, we do not see any need for dramatic military moves.”

A spokesman for China’s Foreign Ministry blamed America’s involvement for causing instability in the region.